It occurs in hay fever sufferers and it is caused by a true allergy to certain fresh fruits, nuts and raw vegetables. Reactions to the same foods when cooked are less likely but can sometimes occur.

In most cases there is only a low risk of progression to a severe reaction.  In a few people, symptoms in the mouth or throat may be caused by other foods such as nuts, shrimp or egg, and for these the risk of progression to a more severe generalised reaction is greater.   People with oral allergy caused by fruits or vegetables often have an associated allergy to certain pollens, and may get hay fever when these pollens are in season.

Pollen food syndrome

This is the commonest form of oral allergy syndrome. A number of pollen allergies may be connected with the condition, although the commonest is birch pollen.  It has been estimated that as many as 75% of birch-allergic patients may be affected by the mildest form, a sensation in the lips or tongue after eating raw apples. However, many sufferers do not realise that they have an allergic problem.  Other pollens involved include grass pollen and certain weed (e.g. mugwort) pollens.

Adults appear to develop this condition more often than children, local reaction to fruits and vegetables being the most frequently encountered kind of food allergy in sufferers over the age of ten.  Children appear more likely to suffer a more widespread kind of allergy (e.g. rash, vomiting or wheeze) as a response to foods such as egg, nuts or seafood to which they are allergic and in them, the oral allergy syndrome and reactions to fruits or raw vegetables is less common.

Symptoms
Redness, swelling and itching, with or without rash (blotchy, pimply or even blistering) of lips, tongue, inside of mouth and soft palate.

Occasionally itchy swelling of the throat may occur. Symptoms in the oesophagus (gullet) or stomach include pain and discomfort, heartburn, nausea and even vomiting.

General symptoms such as urticaria (nettle rash) rhinitis and asthma may occur minutes or an hour or two later, particularly if the sufferer ignores the local symptoms and eats all of the culprit food.

Latex food syndrome

This is another type of oral allergy syndrome. People who react to a particular group of foods may also be allergic to latex, a condition known as the latex food syndrome.  As with the pollen food syndrome, the cause is the presence of similar proteins present in the latex and also in the raw fruits concerned. Latex is the substance collected from rubber trees out of which rubber is made.  Latex balloons, rubber gloves, elastic and certain medical devices may cause symptoms after skin or mouth contact, or sometimes asthma and rhinitis if latex dust (for example in the powder from rubber gloves) is inhaled.  General aspects of allergy to rubber latex are discussed elsewhere.  

A list of the foods that may cause symptoms to sufferers of both latex-fruit syndrome and pollen-fruit syndrome is given below.

Cross reactions

 The more likely culprits are shown in bold type: 

Pollen food syndrome		Cross-reacting foods
Birch		almond, apple, apricot, carrot, celery, cherry, coriander, fennel, hazelnut, kiwi, nectarine, parsley, parsnip, peach, pear, peppers, plum, raw potato, prune, tomato, walnut - occasional patients also react to raw legumes (e.g. pea, green bean, mange tout)
Rye grass		melon, peanut, tomato, watermelon
Latex food syndrome		Cross-reacting foods
Rubber latex		almond, apple, apricot, avocado, banana, raw carrot, raw celery, chestnut, cherry, dill, fig, ginger, kiwi, mango, melon, oregano, papaya, passion fruit, peach, pear, plum, raw potato, sage, raw tomato

Avoidance is the only treatment

The correct identification and avoidance of the culprit food or foods must be the main aim. Previous experience of what has happened when eating certain foods is the most important evidence.  Some foods seem only to cause problems when eaten in the raw state (often the case with carrot and apple) and eating the foods when cooked causes no problem.  Skin and blood tests can help to confirm the diagnosis.  It does not follow that all the foods of a particular group will cause trouble for someone who reacts to one or two of them.  Unless you are advised otherwise, only the foods that have caused symptoms in the past should be avoided.

In addition, you should stay alert to the possibility that further sensitivities to other foods in the same group might develop in the future.  Once you are sure that a particular food is causing symptoms, (and especially if a skin or blood test confirms the allergy) it is better to exclude it in future.

In an occasional case where it is considered that there may be a small risk of severe or generalised reaction a sufferer may be advised to carry adrenaline by injection as a precaution.  In other cases, especially where the throat is involved, an adrenaline aerosol spray may be advised.

Most sufferers have mild symptoms and can generally be reassured that their condition is never likely to become severe, although it is unlikely that they will ever grow out of it.  Desensitisation treatment for this condition is not available at the present time, although it is possible that this form of treatment might become available in the future.